[ExI] Faster than light??

[Alfio Puglisi]

On Mon, Sep 26, 2011 at 4:47 PM, spike <spike66 at att.net> wrote:

>
> On Behalf Of Adrian Tymes
> Subject: Re: [ExI] Faster than light??
>
> On Sat, Sep 24, 2011 at 2:28 AM, Eugen Leitl <eugen at leitl.org> wrote:
>
> > I'd call retrograde signalling in time (which can be indefinite via a
> > chain of routers) and causality violations pretty Earth-shattering.
>
>
> I thought of an example.  Assume FTL signaling is possible, but we don't
> think it is.  A quasar could be a very tight cluster of distant stars
> inhabited by an advanced species.  They emit signals for some reason we
> don't yet understand, perhaps a navigation beacon or something.  A central
> commander gives orders to the outliers to change the emitted signal to such
> and such and sends out the command faster than light.  They all do so.
>  From
> the point of view of all distant non-FTL-hipsters, the cluster of stars
> appears to change in a few light hours when they are actually ordinary
> stars
> spaced over perhaps a few light months, leading the ignorant (us) to assume
> the object is a lot smaller than it really is, and emitting energy from
> that
> small space at an astonishing rate.


No, it wouldn't work. The problem is, if every star in the cluster changes
its luminosity at the same time (according to an observer situated in the
cluster's center), light from the closest star will reach us well before the
light from the stars at the opposite end, along the line of sight. Even if
you assume that a quasar is a spherical object with uniform brightness,
and instantaneous uniform change across its whole surface, light from the
sides will reach us later than light from the point closest to us.
In order to simulate a small space, you would need to coordinate the
luminosity change so that the stars farther from us change before the rest
(again according to an observer at the center of the cluster). Of course,
such a trick would work only in a specified direction, which raises some
questions about what those aliens are up to :-)

Alfio
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